Solid phase organic chemistry (SPOC) which was originally developed for peptide and oligo nucleotide synthesis, is now widely applied as an organic synthesis tool in the preparation of small molecules. The SPOC methods are exploited both by academic and pharmaceutical researchers to produce compounds, in limited number or as part of large libraries, to be submitted to high throughput screening in the search for new leads to address the increasing number of therapeutic targets.
The advantages of SPOC over the solution approach are well recognised (reactions driven to completion by excess reagent, easy purification by filtration and easy automation of the processes) and the limitations as well (not all the reactions are amenable to solid phase, e.g. hydrogenation, traditional analytical methods poorly amenable for in process control, continuous need of developing new synthetic methods).
In addition to the attach-detach steps which need chemistry development, the chemical groups involved both in the linkage and in the spacers sometime pose limitation to the chemistries to be carried out to assemble the desired compound and consequently deserve special attention. In former times the attachment relied on traditional hydrophilic groups such as hydroxy, amine and carboxy taking advantage of the knowledge coming from the protective groups chemistry.
Such handles have clear drawbacks as they are stable only under limited conditions and as a common feature, upon detaching they leave the precursor groups on the final molecule as a trace of the attachment point. Moreover when the anchoring point is on a phenyl ring, the presence of hydroxyl, carboxyl or amino groups may be detrimental from the biological point of view. In many cases these groups negatively affect the interaction with the receptor sites and are responsible for low absorption and fast metabolism when compounds of pharmacological interest are tested in vivo. If considering that a phenyl ring is present at least in 70% of compounds endowed with biological activity it is worthwhile developing methods which allow a phenyl ring to be used as an attachment point and in the same time the released compounds don't show any trace of the anchoring point, unless other groups are desired to expand diversity.